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Hi guys! I would appreciate any input on strange AC behavior. Two techs from two companies provided different results on troubleshooting. Both suggested different strategy on dealing with it. I would call third one, but afraid I will have third opinion and what to do then?

Problem unit is Lenox central AC with very poor performance. Unit is for the second floor and compressor is on the ground and air handler is in the closet of one of the room. High pressure line goes from hot to cold every 8 seconds or so. Low pressure line relatively cold all the time, with condensation on it. Sight glass goes from bubbles to clear and back with about the same rate. High pressure is fluctuating with about the same rate. Gauges show approximate adequate charge. I do not remember exact number, but both techs agreed on charge is not an issue here. Pressures if I remember correctly something 70 low and 200  250 with mentioned fluctuation at 85 degree outside. When first tech came the pressure was a bit lower (about maybe 65psi). Fluctuations were the same. He added freon, but everything stayed the same, just pressure went up. It seems only source of fluctuation pressures/temperature of line are in question. Any ideas? Thanks in advance.

first superheat and subcooling readings would be helpful but it could be a list of things such as txv searching and or dirty coil causing flash gases so this is why we want to know S/H and Subcooling And even outdoor temps.

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what were the sugestions the two differant techs made
also as has been said already need more info
as a guess beenthere i would think is pretty close but could also be a lot of other things to. may also be a defective metering devise or even low on charge
what ever is wrong is not diy friendly

Thank for the input. First of all to answer that I was afraid I get a third different opinion, so you came here where you can get a thousand opinions. I suspected I would have summary of opinions. What most agree on thats would be most probable cause. I do not mind paying the tech, but if two called and both were paid and both suggested different approach, that mean I have to find the right guy before I will drain my wallet. I am out of job and simply cannot afford this now. Now, on subject. Unit is very old. Definitely more than 15 years old. When I bought the house 10 years ago, it was there and looked old even back then. It is approx 2ft by 2ft brown colored lenox. I never saw any similar units anywhere. I cant read plate because all writing is gone on it. One tech said need to replace everything. But then said we may try to recover freon, vacuum everything and then try to fill back with fresh. But no guarantee on that. This mean to me he can not diagnose problem with 100 percent. Is it possible to diagnose if one has equipment (gauges and head I think)? Another said only TXV is bad and needs to be replaced and suggested the same procedure (recover freon and replace TXV then charge back. No guarantee either was given, but I will have to pay, this is granted. I am ready to pay for fixing, just have to know in advance how much it will cost. Obviously replacing everything will make system work. I am just not ready now for this solution. If it can not be repaired, I have to wait couple of months at best. What would be signs of broken beyond repair AC? Compressor seems to be working, right? Is TXV repairable? I mean for pro? Should be refrigerant recovered first or it can be done on charged machine? Thanks in advance!

after rereading your post i am wondering how long has this been happening. my reason for asking is two folded.
first if this has been going on since day one witch i have seen on a few ocassions. the installer when installing the txv did not remove the scharder valve for the equaliizer port. there for the valve is not able to operate properly.
i have had a few units that were about 10 to fifteen years old and picked up on this during a preseason.
high side and low side go up and down equal distant at the same time. or the txv is defective. noncondensable after this lenth of time is not very likely. this is just a guess and not a very likely one either